Morphological examination and transcriptomic profiling to identify prednisolone treatment in beef cattle

In livestock production corticosteroids are licensed only for therapy, nevertheless they are often illegally used as growth promoters. The aim of this study was to identify morphological or biomolecular alterations induced by prednisolone (PDN) in experimentally treated beef cattle, since PDN and its metabolites are no longer detectable by LC-MS/MS methods in biological fluids. Moreover, PDN do not induce any histological alterations in thymus, differently from Dexamethasone treatments. Therefore, a marker of illicit treatment for this growth promoter could be useful. Eight male Italian Friesian beef cattle were administered prednisolone acetate 30 mg day-1 per os for 35 days, while seven beef cattle represented the control group. Six days after drug withdrawal the animals were slaughtered. Morphological and morphometric modifications were evaluated in epididymis and testis, whereas transcriptomic changes induced by PDN administration were investigated in Peripheral Blood Mononuclear Cells (PBMCs) at different sampling times, and in skeletal muscle and testis sampled at slaughtering. In the epididymis, spermatozoa number decreased in PDN treated animals, and in some cases they were totally absent. Correspondently, in testis of treated animals, down-regulation for serine/threonine kinase 11 (STK11) gene expression was detected (p<0.01). DNA microarray analysis revealed a total of 133 differentially expressed genes in skeletal muscle and testis, and 907 and 1,416 in PBMCs after 33 days of treatment and at slaughtering, respectively. Histological investigations on epididymal content could represent a promising marker for PDN treatment in beef cattle, and could be used as a screening method in order to identify animals worthy of further investigation with official methods. Moreover, the clear transcriptomic signature of PDN treatment evidenced in PBMCs supported for the possibility of using this matrix to monitor the illicit treatment in vivo during ranching.